An immunoassay kit for the determination of methadone in serum. Comparison with liquid chromatography.

Therapeutic monitoring of patients participating in methadone maintenance programmes requires the qualitative or quantitative determination of methadone in urine before and during treatment. Generally immunoassay techniques were used for this determination, but more and more often measurement of plasma or serum levels are required by the physician. The possibility of adapting a commercially available FPIA kit (TDX ABBOTT) for urinary assays to the serum determinations was investigated. The specific modifications of the method and the dilution conditions for high concentrations are described. Results were compared with those obtained by liquid chromatography.